A great many performance attributes are demanded of tires. In particular, there is a demand for steering stability during high-speed traveling, stability on wet road surfaces, reduction in rolling resistance to enable greater automobile fuel efficiency, and improvement in friction resistance.
Conventionally, in order to achieve both a reduction in rolling resistance as well as stability on wet road surfaces, in particular, silica is widely used as a reinforcing filler. A typical known technique for improving the dispersibility of silica is to increase the mixing time or to blend a large amount of a silane coupling agent into the silica. However, when the mixing time is increased, the gel content increases excessively, and the rolling resistance is diminished, which is not preferable. When a large amount of a silane coupling agent is blended into the silica, the scorch time becomes too short, and the extrudability of the treads is diminished.
On the other hand, although mercapto-based silane coupling agents increase the dispersibility of silica and improve the physical properties, such agents have the problem that the workability of the silica is diminished. Rubber compositions containing diene rubber, silica, mercapto silane coupling agents represented by specific formulas, and the like have been proposed (for example, Patent Document 1).